"They looked shocked, disorientated, they were supporting each other. The police, ambulances - everyone was on the scene within 10 minutes and they immediately blocked off the piazza. There was a continuous coming and going of ambulances for about an hour after the crash.

"We gave them bottles of water, a place to sit down. We did all we could to help them - as anyone would."

The city's mayor later visited the crash site.

"When I arrived at the scene of the crash and saw it, it was difficult to describe. It is a terrible tragedy," Walter Veltroni told Italian television.

"Obviously, we don't understand why this happened - they are new metro trains so therefore in absolute working order. We have now asked the metro to try to give us the necessary information in order to help understand how something like this could have happened."